Cutting tools of the type that make use of a basic body mountable in a machine or holder, as well as a separate, detachable body, such as a cutting body, may in practice be of the most varying form and not only be rotary tools, such as drills and milling cutters, but also turning tools. In modem machine tools, the basic bodies are so expensive that they, for economical reasons, cannot be integrated with the cutting body, which is a wear part and has a limited service life. In other words, it is profitable to make the proper cutting body in the form of a separate, replaceable unit, which by those skilled in the art usually is denominated “loose top”, and which can be replaced after wear-out, while the basic body can be utilized for a longer time (usually 10 to 20 exchanges). Loose tops having chip-removing cutting edges are manufactured entirely or partly from hard, wear-resistant materials, such as cemented carbide or the like, while the basic bodies are made of a softer material, such as steel or the like. In rotary tools, such as drills and shafts having a cylindrical basic shape, the loose top is connected with the front end of the shaft via some form of interface.
The development of loosetop tools for rotary machining has resulted in a number of different designs for the interface between the loose top and the basic body. By, among others, WO 02/14005 A1, US 2001/0009636 A1 and WO 2004/069457 A1, small milling cutters have been presented in the form of shank end mills or profile mills, which make use of a drawbar, at the front end of which the loose top may be fastened and be drawn into an axial hole in a basic body in the form of a long narrow shaft. In the tool that is accounted for in the first-mentioned document, the loose top is connected with the drawbar via a threaded joint, while the tools according to the two last-mentioned documents make use of hook-shaped members having inclined contact surfaces in order to draw in and fix the loose top in a hole in the basic body. In contrast to such tools the basic bodies of which lack holes for drawing in the loose top (see, for example, U.S. Pat. No. 5,947,660 and U.S. Pat. No. 5,988,953), these tools have the advantage that a rear male element of the loose top is drawn into the hole in the basic body in order to, together with a front portion of the drawbar, be clamped inside a ring-shaped or sleeve-shaped portion of the basic body. Therefore, in such comparatively weak tools as shank end mills and profile mills, the basic bodies of which consist of comparatively slender shafts, a considerably more stable and more reliable anchorage of the cutting body is obtained than in case where the tool lacks holes in which parts of the loose top can be housed.
The fact that loosetop tools have been the object of a large number of proposals for design solutions is in itself evidence that the design of the interface between the loose top and the basic body is a technical problem difficult to master. Thus, consideration has to be given to a number of different factors, which are based not only on the fact that the loose top and the basic body/drawbar are manufactured from different materials and in production units separated from each other, but also on the fact that the tools should operate under severe external conditions, such as strong heat release, etc. In particular, such small tools as shank end mills and profile mills are subjected to a variety of different stresses, which vary most considerably in different functional states. Thus, the loose top, i.e., the hard, detachable cutting body in a profile mill, is subjected not only to axial tensile and compressive forces, respectively, but also to a variety of radial forces acting in different directions. Therefore, to form a working interface between a loose top and a basic body becomes in practice a delicate balance between a number of, at times, conflicting desires.
With the purpose of developing loosetop tools to a greater perfection, an interface acting between the loose top and the basic body has been proposed of the type that is accounted for in the previously filed Swedish patent application SE 0403039-2. In this case, at least one pair of co-operating so-called serration surfaces, which have a certain axial extension and the ridges and grooves of which extend perpendicularly to the longitudinal axis of the tool, are utilized as an interface between the loose top and a drawbar mounted in the basic body. In this way, the capability of the interface to transfer axial forces, such as tensile forces between the loose top and the drawbar, is improved in comparison with the previously known technique.
However, the tool disclosed in SE 0402039-2 is also impaired by imperfections. Thus, it has turned out that the detachable cutting body under certain circumstances risks breaking or being cracked, for example in the area of male elements that connect to the head of the cutting body. Another drawback is that of the shape of the serration surfaces not with absolute certainty prevents erroneous mounting of the cutting body in the front part of the drawbar.
In an embodiment, the present invention aims at further developing cutting tools of the type initially mentioned so far that the tool meets a large a number of requirements, certain of which being conflicting. Therefore, an object of the invention is to provide a tool having an interface formed between the loose top and the drawbar, which in an optimal way resists varying external and internal forces acting in different directions in the interaction of forces that arises not only in connection with the operation of the tool, but also in connection with the mounting and dismounting of the loose top. Thus, the loose top should, in particular when the same consists of a cutting body from a hard material, be able to be subjected to axial tensile and compressive forces as well as radial or lateral forces, the action angles of which to the body may vary in a most irrational way. In particular, a cutting body made from cemented carbide should be able to resist external forces that in conventional, previously known tools frequently cause fracture in the area of the interface. Simultaneously, the internal stresses in such a cutting body should not become too demanding. On the other hand, the strength of the cutting body must not to too high an extent be gained at the expense of the strength and functionality in the drawbar. In other words, the drawbar must not be made so weak that fracture or fatigue arise in the proper drawbar. In an embodiment, the invention aims at providing a rotatable tool, for example a shank-end mill, which in its entirety is well balanced in order to be driven at high rotational speeds without giving rise to vibrations, with the ensuing difficulties, such as heat release and impaired machining precision. Another, object of an embodiment of the invention is to provide a tool that, in spite of good functionality, is easy to manufacture. In other words, it should be possible to produce the tool by means of a minimal number of working operations.